Development of the first blood pressure measuring method can date back to 1896. German pathologist von Recklinghausen found that in the process of measuring blood pressure by inflating and deflating an arm-wrapping airbag, the arm-wrapping airbag may generate a shockwave corresponding to the blood pressure. However, in the aforementioned blood pressure measuring method, a stethoscope is required. Today, with the development of electronic technology, shockwave can be sensed and measured by sensors instead of stethoscopes. That is, the airbag slowly releases its pressure, a sensor can be used to determine the point at which the shockwave sharply increases, which corresponds to the systolic blood pressure, and a point at which the shockwave starts to slow down, which corresponds to the diastolic blood pressure, thereby obtaining the blood pressure of a human subject.
Conventionally, electronic sphygmomanometer uses a pump to pressurize the airbag. Specifically, the systolic blood pressure and the diastolic blood pressure are sequentially measured by using the pump to press against the blood vessels thereby stopping blood flow in the vessels and then gradually release the air in the airbag. However, a conventional electronic sphygmomanometer requires a pump and a pressure release device, and thus resulting in a relatively large overall size. As wearable devices have become increasingly popular in recent years, the addition of a pump and a pressure release device would hinder the miniaturization of wearable sphygmomanometers.